A water treatment process utilizing ozone is one of advanced water treatment processes for purifying waste water, ground water, river water, lake/marsh water, sea water, storage water or the like.
Conventionally, the water treatment process utilizing ozone comprises the steps of dissolving ozone in water and reacting the dissolved ozone with substances to be oxidized in the water.
More specifically, the process employs an aerator plate disposed at the bottom of a large water vessel to diffuse fine bubbles of ozone in the water. In order to dissolve as much ozone as possible, the greatest possible water depth is provided while the bubbles are made as fine as possible. In practice, however, the depth is limited to 5 m to 6 m at the maximum and the size (diameter) of the bubble to about 20 .mu.m at the minimum.
The process requires an ozone residence time of about 8 minutes to about 10 minutes for the reaction and a large-scale system such as having an ozone dissolution vessel and the like.
Even with such a system, the utilization factor of ozone is only about 60% to about 80%.
Where water containing inorganic substances to be oxidized such as soluble iron and manganese and organic substances is to be treated, inorganic substances more susceptible to oxidization are first oxidized by ozone injected into the water, so that the decomposition of the organic substances by oxidation is slowed.
This is because the oxidization of the inorganic substances entails production of colloidal substances which consume ozone. Accordingly, the amount of ozone used in a process for the decomposition of the organic substances reaches several times an amount required for the intended treatment.
Although the aforesaid problem may be solved by injecting ozone again after removal of the colloidal substances, the colloidal substances have particle diameters on the order of submicron and are difficult to be removed as they are.
Therefore, a need exists for adding a coagulant to increase particle diameters of the colloidal substances for separation and removal thereof.
Such a treatment requires additional facilities such as a reaction vessel and an apparatus for adding the coagulant. Furthermore, the addition of the coagulant results in an increase of waste products.
In view of the foregoing, it is an object of the present invention to provide a simplified water treatment process and system which are capable of purifying water without addition of a coagulant and offer an improved use efficiency of ozone.